A Tour of the Cell Chapter 6

n n Objectives F F Distinguish between a prokaryotic and eukaryotic cell F F Describe the unique structures of a prokaryotic cell F F Describe the structural differences between plant and animal cells F F Describe the complex structural and functional interconnections among the organelles of the endomembrane system F F Describe the structure of the eukaryotic nucleus, mitochondrion and chloroplast

F F Describe the surface structures of the cell that provide support, protection, and movement in, and communication with, the extracellular environment

Introduction n n Cell is smallest functional unit of life F F cell theory: all organisms composed of cells all existing cells arise from pre-existing cells n n Common characteristics of all cells: u u cell contents surrounded by plasma membrane u u cytoplasm consists of semifluid matrix u u organelles are embedded in cytoplasm u u contain genes in the form of DNA

Fundamental Features of Life n n Features of cells are characteristic of life u u cells are highly structured u u cell structure and function are related u u cell membranes separate the cell from the external environment u u each cell has DNA as the genetic material u u each cell carries out metabolism

Cell Organization n n Two types of cells-prokaryotic and eukaryotic n n Prokaryotic: u u small u u lacks nucleus; DNA in nucleoid region u u cytoplasm surrounded by plasma membrane and outer cell wall u u flagella and pili may be present

Cell Organization n n Eukaryotic u u Larger than prokaryotic cells u u complex internal structure with membranous and non- membranous organelles u u Membranous components: nucleus, endoplasmic reticulum, Golgi apparatus,mitochondria, lysosomes and peroxisomes u u Non-membranous components: ribosomes, microtubules, centrioles, flagella and cytoskeleton

Plant vs. Animal Cells u u Animal cells surrounded by plasma membrane only u u Plant cells surrounded by plasma membrane and rigid cell wall; also have central vacuole and chloroplasts

Eukaryotic Cell Organization n n Eukaryotic organelles form four functional groups: u u manufacture u u breakdown u u energy processing u u support, movement and communication

Manufacturing n n Nucleus is cell’s genetic control center u u surrounded by double membrane F F contains pores to allow passage of material between nucleus and cytoplasm u u DNA normally present as strands of chromatin u u During cell division, chromatin coils up to form chromosomes u u Nucleolus-organelle within nucleus-responsible for ribosomal RNA synthesis

Endomembrane system n Collection of membranes either inside or surrounding the eukaryotic cell, related through direct physical contact or by transfer of vesicles

Endomembrane system n n Endomembrane system: RER and SER u u Rough endoplasmic reticulum contains ribosomes; protein synthesis ( RER) u u Smooth endoplasmic reticulum synthesizes lipids, processes materials, acts as storage and detoxifies substances (SER)

Golgi n n Golgi apparatus recieves products from ER n n Chemically modifies the products sent to it n n Puts “Zip Codes” on products so they know where to go in the cell n n Puts these modified products in vesicles and sends them out

Golgi n The Golgi Apparatus is the “UPS” of the cell n Its recieves, warehouses, sorts, modifies, packs and reships substances

Lysosomes n n Lysosomes contain enzymes to digest substances and wastes; defective lysosomes cause fatal diseases n n Lysosomes help your cells recycle materials: Each Liver cell recycles half of its synthesized macromolecules per week n n Whey else do they do?

Vacuoles n n Vacuoles function in general cell maintenance n n In plants they can hold organic substances n n In protists vacuoles can hold food or water, or act as pumps

Energy Processing n n Mitochondria: u u found in all eukaryotic cells, except anaerobic protozoans u u surrounded by double membrane u u site of cellular respiration u u Prokaryotes don’t have them… What do they do?? u u Inner and outer membrane u u Matrix and Cristae

Chloroplasts n n Chloroplasts: u u found in plants and algae u u convert solar energy to chemical energy u u Surrounded by double membrane u u site of photosynthesis u u More on these organelles in Ch 10

Peroxisomes n What is the function of Peroxisomes? n Read all about them in your book n What is the difference between the terms detoxification and degredation???

Support, Movement, and Communication n n Internal cell skeleton-cytoskeleton u u composed of 3D meshwork of proteins u u rods of globular proteins-microfilaments F F ropelike strands of fibrous proteins-intermediate filaments F F hollow tubes of globular proteins-microtubules u u microtubules provide anchors for organelles, act as conveyor belts and form cilia and flagella

n n Cilia and flagella u u function to move whole cell u u structure consists of 9 microtubule doublets arranged around central pair (9+2)

n n Movement of cilia and flagella occurs when arms consisting of the protein dynein move the microtubule doublets past each other

n n Microfilaments cause contraction of muscle cells n n They also function in ameboid movement, cytoplasmic streaming and support for cellular projections

Centrioles n n Centrioles, located adjacent to the nucleus, anchor and organize the microtubules that form the spindle during cell division

Eukaryotic Cell Organization n n Cell surfaces u u protect, support and join cells u u in plants, neighboring cells joined to form interconnected and coordinated group F F cell walls multi-layered, composed of mixtures of polysaccharides and proteins F F plasmodesmata-channels through cell walls connecting cytoplasm of adjacent cells- plants

Extracellular Matrix u u in multi-cellular animals cells often surrounded by sticky mixture of polysaccharides and proteins u u Extends outward from the cell membrane u u Lots of collagen is found there……

Eukaryotic Cell Organization n n Several type of junctions between cells: F F tight junctions: leak proof; block movement of substances F F anchoring junctions- join cells and provide structural support; like the rivets in your blue jeans F F communicating junctions ( gap junctions)-provide channels between cells; allow rapid transport of materials